Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay of ^5_ËHe and ^12_ËC

C. BARBERO, F. KRMPOTIC AND A.P. GALEAO

Brazilian Journal of Physics

SOCIEDAD BRASILEIRA DE FISICA

Año: 2006 vol. 36 p. 1 - 6

We analyze the influence of sigma meson exchange on the main nonmesonic hypernuclear weak decay observables: the total rate, Gamma_{NM}, the neutron-to-proton branching ratio, Gamma_{n/p}, and the proton asymmetry parameter, a_Lambda. The sigma meson exchange is added to the standard strangeness-changing weak Lambda N -> NN transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octet (pion, eta, K, rho, omega, K^*). Using a shell model formalism, the $sigma$ meson weak coupling constants are adjusted to reproduce the recent Gamma_{NM} and Gamma_{n/p} experimental data for ^5_{Lambda}He. Numerical results for the remaining observables of ^5_{Lambda}He and all the observables of ^{12}_{Lambda}C decays are presented. They clearly show that the addition of the sigma meson improves the agreement with the data. However, its effect it is not enough to reproduce well a_Lambda values, which means that another improvements of the model must be explored to explain the puzzle posed by the experiments.